It is important to diagnose the pathogen as quickly as possible to accelerate the start of appropriate treatment of patients with infectious diseases. Recently, rapid diagnostic tests improve the accuracy of diagnosis of the pathogen. Furthermore, it is also available to do the test with very simplified method by using portable kits. Many PCR and antigen detection techniques have been developed to improve the diagnosis of specific pathogens, such as influenza virus, Legionella, Chlamydia, Mycoplasma, Helicobacter pylori and Mycobacterium tuberculosis. Especially, urinary antigen detection kits are useful at the site of outpatient clinics.